Electrical generators containing one or more superconducting components are known to those skilled in the art. Thus, for example, in U.S. Pat. No. 4,740,724 of Arata Masanori et al., a superconducting generator rotor which has a superconducting field coil cooled by liquid helium (at a temperature of 4.2 degrees Kelvin) is disclosed. The electrical generator of this Masanori et al. patent is not practical, for it must be operated at an economically inefficient temperature of 4.2 degrees Kelvin.
In U.S. Pat. No. 4,583,014, John H. Murphy et al. disclose a dynamoelectric machine with a rotor having a superconducting field winding and a damper winding. The device of this patent also must be operated under liquid helium and, thus, is not economically viable.
If one were able to modify the devices of the aforementioned patents so that they utilized coils consisting of "high Tc" superconductive material, it theoretically might be possible to operate the generators at higher temperatures. The "high Tc" superconductors exhibit superconductive properties at relatively high temperatures, often as low as 77 degrees Kelvin.
However, many problems have been encountered in efforts to make coils consisting of "high Tc" superconductive material. Thus, for example, in an article by R. F. Giese et al entitled "High Temperature Superconductors: Their Potential for Utility Applications" (Department of Energy Report DE90 009704, CONF-901062-1, 1990), the authors disclosed that "HTSC wires operating at 77K have the potential for carrying the large currents . . . . However, to date, short samples of such wires have yielded much lower current density, which falls off rapidly with increasing magnetic fields. These lower values are believed to be due to the following two factors: (1) the penetration and subsequent movement of flux vortices . . . (2) the difficulty of the superconducting current in crossing grain boundaries . . . . "
It is an object of this invention to provide an electrical generator containing a superconductive stator which can be efficiently operated at a temperature as high as 77 degrees Kelvin.
It is yet another object of this invention to provide an electrical generator which does not require the presence of a coil comprised of high Tc superconductive material.
It is yet another object of this invention to provide an electrical generator in which energy losses due to mechanical contact and friction are minimized.